Purification procedures that appear to be generally applicable to invertebrate MTs have only recently been developed and are described here. Thus far, few invertebrate MTs have been purified and characterized, although proteins that exhibit similarities to MT have been identified in numerous invertebrate species. A greater understanding of MTs of this group, which comprises most of the animals in the animal kingdom, will provide the basis for increased understanding of the evolution of this ubiquitous protein. Additionally, specific invertebrate species may provide useful models for probing MT function and contribute to a greater understanding of the biological role of MT.